Strange disease liquidates sea star population. Human activity could be at fault, says a biologist

A disease that makes organisms to rot alive. Sea star wasting disease effects sea stars on the west and recently also on the east coast of the United States. There isn’t much known about this disease. The research is very expensive and new discoveries often lay in the hands of students who want to save decimated sea star population.

Noëlle Wisneski and her fellow students from the University of New England in Maine want to find the roots of the sea star wasting disease which is killing off the sea star population in great numbers. In this interview, we’ve asked Noëlle how does a sea star research look like and what are the signs of this disease

How does one research sea stars?

When we do research, we go out into the low tide and we do transects. That means that we are gathering data about the density of sea stars. The density of sea stars correlates with the prevalence of the disease. The more sea stars are there, the more of disease. When we find sea stars we examine them, and we take a few backs into the lab. We focus mostly on finding signs of sea star wasting disease.

What is known about the sea star wasting disease?

There is not much known about this disease. All we know is that it’s probably a virus or bacteria. It causes the limbs of a sea star to rot off. It’s not natural, sea stars and echinoderms can lose their limbs and grove them back, they can also detach them at will. But with this disease it’s different. Something happens with the vascular tissue or the central ring. The central ring is part of the sea star’s nervous system. It runs through each of the arms and around the mouth. The nerves help to move the arms of the sea star. If the nerves are damaged, then the limbs can’t move. The disease also causes the tissue to rot. This causes the nerve in the arm to rot too. With the nerve and the remaining tissue rotting away the arm cannot grow back.

Do you not know the cause?

We are not entirely sure what causes it yet. All we know is that it’s mostly found on the west coast of the United States. More specifically on the coast of Alaska and Washington. Now it’s also found on the east coast, in Maine though. That`s why we are concerned because we don`t know how it got here and it might wipe out the entire species of sea star population. What makes it even more interesting is that studies done on the west coast have found that it is typically caused by bacteria. Though the wasting disease on the east coast has characteristics of a virus.

There have been major mortality events in the past caused by weather. Is weather a concern in this situation as well?

We are in El Nino right now – as we did in the nineties – so we think it might have something to do with it. But we are still unsure. We are having different weather these past few years. The winters and the summers are more intense. Researchers on the west coast of the United States are finding that locations affected by wasting disease had warmer waters than before.

How did the disease get to the east coast?

We have several theories. We believe that it got to the east coast through some invasive species. Someone might have brought an infected sea star to our coast from the west coast. We are not so sure. It’s been suddenly found about three years ago. It’s a very new situation and it’s very alarming.

How did you first find the disease?

We had sea stars in a tank in our lab and we were going to be using them for a dissection to look at their vascular tissue. And then suddenly over the weekend, they all died. It was very quick, and it spread from one sea star tank to the next one. The tanks are open, so the sea stars can crawl into another tank. Then we cleaned up the entire tank and we collected a new population, we thought it might be something in the water. But the same thing happened again.

What is special about sea stars that it only affects them?

Its similar to people. They are the only species that can get the flu, and sea stars are the only ones that can be affected by the sea star wasting disease. You don`t really see dogs getting a stomach bug, do you? It affects some species more than others though. The common sea star, for example, seems to be the most affected.

How come that certain individuals seem to be immune towards this disease?

We are still trying to figure it out. We took a very thin slice of a healthy sea star tissue and ran it through PCR. This is a method for analyzing the DNA where you can sequence it. But all we have now is data on the healthy sea stars. The disease seems to be more of a springtime issue. When we went hunting for them in the summer we didn’t find any diseased ones. In spring we found all diseased ones. It’s very mysterious, it’s hard to crack. Very little is known about it because there has been very little research made.

What are you expecting to find?

We are hoping to find the cause. Maybe there is a human impact and there might be something we can do to stop it. We want to find out if the disease has something to do with increasing ocean acidity, which humans are causing. But if it’s just a normal disease, obviously, there is nothing we can really do to stop it. Unless we physically took the effected population and moved them somewhere else that is.

The ocean acidity affects mostly organisms that have calcium carbonate shell. Does it affect sea stars in a similar way?

They do, they have a harder exoskeleton and the acidification does wear and tear on them. It’s obviously not as prevalent as in species that have actual hard outer shell, but ocean acidification affects all invertebrates really because they live in the water and acidity slowly eats on them. They can`t adapt fast enough and even a small increase can cause a change. It can change what they eat, when they mate, how they mate, how many males versus females are born. It can affect everything.

Which places are most affected?

Mostly west coast. And they are mostly doing it to themselves though. It doesn’t seem like something else is giving them the disease. Sometimes they eat limbs of other affected sea stars. But they don’t seem to catch the disease from that.

What variables play a role in a set of data?

The weather conditions are important. In a sunny high tide, there might be more starfish than in other weather. We are trying to collect data of those factors. We are writing down where we did the transacts, how big of an area we covered. We note how many animals we find in each location because as I said, their number correlates with the spread of the disease. One set of data can look like this: sunny, low tide, we went to the rocky shore and we covered ten meters square, but we only got three sea stars. Right now, we are mostly doing density data research. We did some DNA tests, but it`s very expensive, as well as time-consuming, so we need to get a grant first. One DNA test can cost some thousand dollars.

Noëlle Wisneski (*1997) comes from a town of South Windsor, Connecticut. She is studying marine biology at the University of New England where she researches sea stars.

 

Tomáš Hrivňák

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